Network interface devices permit a subscriber to access a variety of information via a network. A passive optical network (PON), for example, can deliver voice, video and data among multiple network nodes, using a common optical fiber link. Passive optical splitters and combiners enable multiple optical network terminals (ONTs) to share the optical fiber link. Each ONT terminates the optical fiber link for a residential or business subscriber, and is sometimes referred to as a subscriber premises node that delivers Fiber to the Premises (FTTP) services.
An ONT is connected to one or more subscriber devices, such as televisions, set-top boxes, telephones, computers, or network appliances, which ultimately receive the voice, video and data delivered via the PON. In this manner, the ONT can support telephone, television and Internet services. An ONT is an example of a network interface device. Other examples of a network interface device, in different network types, are cable modems and digital subscriber line (DSL) boxes.
Network interface devices in a cable or hybrid network may be connected to power provided by a central office, which commonly utilizes battery and generator back-up power to maintain a continuous power supply. In contrast, an ONT in an all-fiber optical network is ordinarily powered locally at the subscriber premises. An ONT may receive power from an uninterruptible power source (UPS) unit mounted within or outside the subscriber premises.
The UPS unit may provide back up power during a power outage to maintain critical services, such as voice service. The UPS unit obtains AC power from line power within the subscriber premises and generates DC power for use by the ONT. Hence, the UPS unit is coupled to the ONT via a DC power line and to line power within the subscriber premises via an AC power line. The UPS unit also includes a battery to support backup power when AC line power is unavailable.